1. Field of the Invention
This invention relates to a positioning apparatus in combination with a nuclear reactor to provide for the maintenance and inspection of certain nuclear reactor components within the containment building.
During the periodical refueling operations in nuclear reactors of the pressurized water type, contents of the pressure vessel are removed in groups and stored within the containment building in assigned areas. Thus, the upper internals of the reactor, together with control rod assemblies (clusters) are transferred from the reactor pressure vessel into the upper internals storage pit where these components are supported on a storage stand installed in the storage pit. The invention utilizes the refueling outage of the nuclear reactor to perform inspection and maintenance work on the rodlets of the control rod clusters and components of the upper internals while the latter are stowed in the upper internal storage pit. A periodic inspection of the rodlets after their installation has not been routinely performed; for any inspection work the control rod clusters have been entirely removed from the internals.
2. Description of the Prior Art
U.S. Pat. No. 4,217,173 to Jabsen discloses a nuclear reactor inspection device which includes a carriage and beam construction mounted on the top edge of a reactor vessel and which is adapted to raise and lower vertical scanner tubes to be aligned with desired fuel rods in the reactor core, for inspecting the structural integrity of the nuclear reactor fuel rods without the need of dismantling the fuel assemblies.
U.S. Pat. No. 4,048,009 to Weilbacher discloses a vertically displaceable carriage on which measuring instruments are mounted for checking dimensions of individually positioned control rod extensions in a cooling pit during periodical preventive maintenance checks.
U.S. Pat. Nos. 4,169,758 to Blackstone et al. and 4,311,556 to Iwamoto et al. disclose apparatuses for inspecting the internal surface of a nuclear reactor vessel. The apparatuses are supported above the reactor vessel and are rotatable about a circular track and are radially displaceable in the horizontal direction relative to the circular track and are also movable vertically. On the vertically movable component an additional mechanism for further horizontal and angular displacements is provided which supports inspecting instruments.
U.S. Pat. No. 4,464,332 to Boisseuil et al. describes an apparatus for verifying rod spacings in a nuclear fuel assembly. The apparatus is vertically movable parallel to a vertically positioned nuclear fuel assembly and has components which are displaceable in horizontal directions. The apparatus is designed to verify new fuel assemblies after their manufacture.